A novel approach for temperature control in ISF supported by laser and resistance heating

Aeronautical applications often require small batches of large-scale sheet metal parts made from titanium and its alloys. Due to the low formability of titanium at room temperature, warm forming processes are necessary. Incremental sheet metal forming (ISF) is suitable for production of prototypes and small batches as well as large-scale parts. A short review of the experimental work done by international scientists in the field of warm ISF including stationary and moved temperature sensors will be presented mostly applied from the backside of the sheet metal. The present paper shows a new approach for a tool setup including a thermocouple inside of the tool. Hence, the sensor for temperature measurement was moved with the forming zone. Furthermore, a suitable closed loop control including a PID controller will be presented. The characteristics of the controller will be discussed. By means of two different warm ISF processes (ISF with resistance heating and laser-assisted ISF), the applicability of the developed setup will be analysed and evaluated. It will be shown that the experimental setup is capable to ensure minimal temperatures needed to ensure adequate formability of Ti grade 5.     

Two-directional toolpath correction in single-point incremental forming using model predictive control

Incremental sheet forming (ISF) is an emerging forming technology that promises high flexibility and formability. These properties make it suited for small-scale and customised production. However, the poor geometric accuracy of ISF limits the wide application of this flexible forming technology. This paper presents a two-directional toolpath correction approach to enhance ISF forming accuracy using a model predictive control (MPC) algorithm. A toolpath optimisation method for vertical toolpath correction has been validated in our previous work (Lu et al., Int J Adv Manuf Technol 72:1–14, 2015), and it helps to reduce errors in the base of the test shapes to a suitable level while its major limitation is that horizontal geometric errors are relatively large. This paper extends our previous work (Lu et al., Int J Adv Manuf Technol 72:1–14, 2015) by augmenting the vertical control module with a new control module for horizontal toolpath correction. The proposed control algorithm was experimentally validated in single-point incremental sheet forming (SPIF) using two forming case studies. In the first case study (a truncated pyramid), two control approaches with different assumptions for the horizontal springback distribution along the horizontal cross-sectional profile were tested and compared. Then, the developed MPC control algorithm was applied to form a more complex asymmetric shape. The results show that the developed strategy can reduce the forming errors in the wall and base of the formed shape compared to the existing works. The ISF process with MPC control leads to significant accuracy improvement in comparison with the typical ISF process that is without toolpath control.     

Part accuracy improvement in two point incremental forming with a partial die using a model predictive control algorithm

As a flexible forming technology, Incremental Sheet Forming (ISF) is a promising alternative to traditional sheet forming processes in small-batch or customised production but suffers from low part accuracy in terms of its application in the industry. The ISF toolpath has direct influences on the geometric accuracy of the formed part since the part is formed by a simple tool following the toolpath. Based on the basic structure of a simple Model Predictive Control (MPC) algorithm designed for Single Point Incremental Forming (SPIF) in our previous work Lu et al. (2015) [1] that only dealt with the toolpath correction in the vertical direction, an enhanced MPC algorithm has been developed specially for Two Point Incremental Forming (TPIF) with a partial die in this work. The enhanced control algorithm is able to correct the toolpath in both the vertical and horizontal directions. In the newly-added horizontal control module, intensive profile points in the evenly distributed radial directions of the horizontal section were used to estimate the horizontal error distribution along the horizontal sectional profile during the forming process. The toolpath correction was performed through properly adjusting the toolpath in two directions based on the optimised toolpath parameters at each step. A case study for forming a non-axisymmetric shape was conducted to experimentally validate the developed toolpath correction strategy. Experiment results indicate that the two-directional toolpath correction approach contributes to part accuracy improvement in TPIF compared with the typical TPIF process that is without toolpath correction.     

Effects of forming parameters on temperature in frictional stir incremental sheet forming

Frictional stir Incremental sheet forming (ISF) is a new technology used to fabricate parts of hard-to-form materials without using heating equipment. Thus far, limited information is known about the effects of main forming parameters, except spindle speed of the tool, on the temperature of formed sheet in friction-stir ISF. The effects of six forming parameters, namely, sheet thickness, tool vertical step, tool diameter, spindle speed, feed rate, and wall angle of the formed part, were identified using the design of experiment of orthogonal array, analysis of response tables and graphs, and analysis of variance. Results show that spindle speed, feed rate, sheet thickness, and tool vertical step significantly affect the temperature of the sheet. In addition, the temperature of the sheet is significantly increased by increasing sheet thickness, tool vertical step, and spindle speed but significantly decreased with increasing tool feed rate.

     

圆锥滚子轴承轴向定位预紧刚度计算

研究轴向定位预紧状态下圆锥滚子轴承的刚度计算方法。首先，由轴向载荷作用下轴承内外圈相对位移及力平衡关系，推导圆锥滚子轴承的轴向刚度计算公式；其次，由轴向定位预紧轴承受径向载荷时各滚子的变形，推导出轴承的径向刚度计算公式；并且，经合理近似给出上述径、轴向刚度公式的简便计算公式，最后，将公式的计算结果同实验数据作对比，表明公式的误差较小，可以实际应用。     

高温加热对于纯铝薄膜表面结构的影响研究

在半导体材料中,金属薄膜尺寸缩小会使通电时的电流密度升高而导致材料焦耳热迅速增加,从而影响金属薄膜表面结构。针对纯铝薄膜进行了高温加热试验,模拟实际运行中的温度影响,并分析了影响机理。试验结果表明随着加热温度和加热时间的增加会使铝膜表面原子迁移能力增强,单位时间内原子积聚数量增加,从而导致小丘数量和体积增大。     

A real time marking inspection scheme for semiconductor industries

The deformation and densification behaviour of sintered hypo-eutectoid steel ring preforms with carbon contents of 0.35% and 0.65%, under cold axial deformations, have been studied in order to understand the influence of various forming parameters such as flow stress and percentage axial height reduction on the densification process. Four different conditions of material deformations, namely, pure upsetting, deformation constrained along radial inward direction, deformation constrained along radially outward direction and, finally, deformation of material and pores constrained along both inward and outward radial directions have been applied during the axial cold forming tests. Results of the investigations have established that highest densification rate is achieved in rings subjected to the most severe flow constraint of fully restrained radial flow, at comparatively lower levels of axial deformations. Both carbon content and initial sintered ring geometry are also found to influence the deformation as well as densification rates during the cold forming process. Ring preforms of lower initial geometry, namely, 6:3:2 exhibit better densification rates irrespective of the mode of flow, but require lesser flow stress values, compared to those of initial geometry of 6:3:4. The densification process is observed to follow an almost linear trend in the case of fully constrained axial deformation, whereas, under less severe flow constraints, the same is observed to follow second or third order polynomials.     

Electrosurgical dispersive electrodes heat cutaneous and subcutaneous skin layers

Electrosurgical return electrodes can produce heating, and occasionally burns, of cutaneous and subcutaneous skin layers. Up to now, only limited aspects of modern, dispersive, polymer electrodes have been studied using infrared thermography and thermocouples. This report presents new results on a quantitative infrared study, and adds the aspects of subcutaneous effects using microwave thermography as a third dimension. In agreement with previous work in infrared thermography, average cutaneous temperature increases observed in a dozen human volunteers were 1.5 degrees C for the normal mode, and 5.7 degrees C at near-fault (with partial contact). The intradermal and/or subcutaneous microwave thermographic images exhibited slightly lower, but still significant temperature elevations which were located at a more leading location, and were more widespread. This significant heating of subcutaneous layers, particularly of the sensitive stratum germinativum, clearly suggests the need for multiple-depth (microwave and infrared) thermography in order to evaluate the thermal performance of dispersive electrosurgical return electrodes.     

Formation mechanism and modeling of surface waviness in incremental sheet forming

Improving and controlling surface quality has always been a challenge for incremental sheet forming (ISF), whereas the generation mechanism of waviness surface is still unknown, which impedes the widely application of ISF in the industrial field. In this paper, the formation mechanism and the prediction of waviness are both investigated through experiments, numerical simulation, and theoretical analysis. Based on a verified finite element model, the waviness topography is predicted numerically for the first time, and its generation is attributed to the residual bending deformation through deformation history analysis. For more efficient engineering application, a theoretical model for waviness height is proposed based on the generation mechanism, using a modified strain function considering deformation modes. This work is favorable for the perfection of formation mechanism and control of surface quality in ISF.     

A new mathematical model for predicting the diameter expansion of flat ring in radial–axial ring rolling

An accurate prediction for the diameter expansion is quite essential for the ring rolling with large diameter since it determines the compatibility between the work rolls and the deformed ring in kinematics, so that the rolling stability and the final forming quality of the ring are influenced. A new mathematical model for predicting the diameter expansion of the flat ring in the radial–axial rolling process has been proposed, in which the variation of cross section, the particularity of initial rolling phase, and the effect of slip are all taken into consideration. Based on the proposed mathematical model, a 3D-FEM model for the radial–axial ring rolling process has been developed, and the corresponding experimentation has also been carried out. The diameter expansion in the simulation shows a good agreement with that in the experimentation. The forming quality comparison concerning the circularity, coaxiality, and tilting of the rolled ring has been executed between the former and new proposed method. The result indicates that the new mathematical method is very helpful to control the forming stability and hence improve the ring rolling quality significantly.     

X-ray diffraction in the pulsed laser heated diamond anvil cell

We have developed in situ x-ray synchrotron diffraction measurements of samples heated by a pulsed laser in the diamond anvil cell at pressure up to 60 GPa. We used an electronically modulated 2-10 kHz repetition rate, 1064-1075 nm fiber laser with 1-100 μs pulse width synchronized with a gated x-ray detector (Pilatus) and time-resolved radiometric temperature measurements. This enables the time domain measurements as a function of temperature in a microsecond time scale (averaged over many events, typically more than 10,000). X-ray diffraction data, temperature measurements, and finite element calculations with realistic geometric and thermochemical parameters show that in the present experimental configuration, samples 4 μm thick can be continuously temperature monitored (up to 3000 K in our experiments) with the same level of axial and radial temperature uniformities as with continuous heating. We find that this novel technique offers a new and convenient way of fine tuning the maximum sample temperature by changing the pulse width of the laser. This delicate control, which may also prevent chemical reactivity and diffusion, enables accurate measurement of melting curves, phase changes, and thermal equations of state.     

Effects of process parameters on force reduction and temperature variation during ultrasonic assisted incremental sheet forming process

The incremental sheet forming (ISF) is an innovative dieless forming process featured with high formability and short lead time which is suitable for rapid prototyping and small volume production. The integration of ultrasonic (US) vibration into the ISF process can significantly reduce the forming force and bring other benefits. In this work, the impacts of process parameters including the sheet material, US power, feeding speed, and tool diameter, on force reduction and temperature increment were studied. The force reduction contains two components—the stress superposition-induced force reduction and acoustic softening-induced force reduction. The stress superposition-induced force reduction was analyzed by finite element simulation while the total force reduction was detected by experiments since currently, the unknown mechanism of the acoustic softening cannot be modeled. The temperature increment was measured by a high-speed infrared camera. The results show that the force reduction can go up to 56.58% and the temperature increment can be as high as 24.55 °C. In general, the material with a higher yield stress results in a higher force reduction and a higher temperature increment. A higher US power or a lower feeding speed can significantly enhance the force reduction and the interface temperature increment. The tool with a smaller diameter has a comparable effect as a larger tool, but a larger vibration amplitude is required.     

基于收发分体声波换能器的二维温度场重建

基于声学测温原理,运用发射端和接收端之间的声波信号飞行时间进行温度场重建,是工业应用领域中燃烧或加热处理过程温度测量的研究热点。本文采用收发分体声波换能器,确定其合理安装方式,运用Markov径向基拟合待测区域的声速分布,通过声速矩阵的奇异值分解,反演计算出温度场。仿真实验中设计了复杂程度不同的4种模型温度场,并考虑声波飞行时间在不同水平下的测量误差对重建结果的影响;实际测试中验证了本文方法在室温无加热、单峰对称、单峰偏斜的温度分布下的重建效果。实验结果表明,本文提出的收发分体声波换能器安装方式结合基于Markov径向基拟合的重建算法,在温度场重建中具有较高的精度和较强的抗干扰性。     

牙轮钻头径向非对称扁平密封性能研究

为了提高HAR橡胶密封圈寿命,提出一种新的径向非对称扁平密封结构。相比传统对称截面扁平密封圈,径向非对称截面的密封接触面积更小,因而减小了内圈动密封面旋转产生的热量以及磨损。通过试验对比氢化丁腈橡胶(HNBR)与丁腈橡胶（NBR）的性能,选择出合适的橡胶密封圈材料;分别建立径向非对称扁平密封圈与传统对称截面扁平密封圈的有限元模型,对比2种结构的密封性能;在不同的环境压力和温度下对径向非对称扁平密封圈的密封性能进行评价,并在现场进行应用验证。仿真结果表明：径向非对称扁平密封圈接触应力更大,密封性能更优;同时,其Mises应力明显低于传统对称截面扁平密封圈,证明径向非对称扁平密封更适合长期稳定工作。现场应用结果同样验证：在高温高压工况下,径向非对称扁平密封圈密封性能可靠,具有较高的实用价值。     

飞轮储能系统中径向永磁轴承的设计研究

为解决飞轮系统中因轴承摩擦导致的能量损耗问题,设计了一种可以应用于飞轮系统的径向永磁轴承.分别利用Yonnet简化数学模型和有限元分析软件ANSYS Workbench,对轴承中的磁环进行了承载能力的计算和分析.结果表明,磁环所受径向力随磁环厚度、径向偏移量增加而增加,但其增加关系有所不同;另外,随着轴向偏移的增大,径向力逐渐减小、轴向力迅速增大.     

冷滚打成形中滚打深度与回弹规律的仿真

为了有效地控制回弹对成形件精度的影响,针对变形量与回弹量之间的关系进行研究。依据冷滚打成形的基本原理,应用ABAQUS软件建立了有限元动态仿真模型,通过仿真获得了不同滚打深度下成形齿槽截面在切向、轴向和径向的变形规律与回弹量。由于动态仿真后工件内部的力处于不平衡状态,不能直接进行回弹求解,所以在动态仿真结果的基础上建立了静态仿真模型,通过静态分析获得了不同滚打深度成形齿槽截面各部分在切向、轴向和径向的回弹规律。在改装的实验设备上进行冷滚打成形实验,获得了工件廓形,并将其与相同工艺条件下的仿真结果进行比较,验证了仿真结果的正确性,为有效控制回弹对成形精度的影响提供了参考。     

Plastic Deformation Mechanism in Double-Roller Clamping Spinning of Flanged Thin-Walled Cylinder

Double?roller clamping spinning(DRCS) is a new process for forming a thin?walled cylinder with a complex surface flange. The process requires a small spinning force,and can visibly improve forming quality and production e ciency. However,the deformation mechanism of the process has not been completely understood. Therefore,both a finite element numerical simulation and experimental research on the DRCS process are carried out. The results show that both radial force and axial force dominate the forming process of DRCS. The deformation area elongates along the radial direction and bends along the axial direction under the action of the two forces. Both the outer edge and round corner of the flange show the tangential tensile stress and radial compressive stress. The middle region shows tensile tangential stress and radial stress,while the inner edge shows compressive tangential stress and radial stress. Tan?gential tensile strain causes a wall thickness reduction in the outer edge and middle regions of the flange. The large compressive thickness strain causes material accumulation and thus,an increase in the wall thickness of the round corner. Because of bending deformation,the round corner shows a large radial tensile strain in addition. The inner edge of the flange shows small radial compressive strain and tensile strain in thickness. Thus,the wall thickness on the inner edge of the flange continues to increase,although the increment is small. Furthermore,microstructure analysis and tensile test results show that the flanged thin?walled cylinder formed by DRCS has good mechanical properties. The results provide instructions for the application of the DRCS process.     

Numerical simulation of electric hot incremental sheet forming of 1050 aluminum with and without preheating

Incremental sheet forming (ISF) consists of deforming the sheet, through a spherical punch, punctually and progressively until it reaches the desired geometry. Compared to the conventional process, the ISF can achieve much higher levels of formability. But the stresses and residual strains are often pushed to the limit on the path, producing a piece with brittle behavior, which is not desirable for applications in engineering. To work around this inconvenience, one solution would be to perform the conformation at high temperatures, a process known in engineering as hot forming. This study aims to evaluate the behavior of the state of stresses and strains in the hot incremental sheet forming of 1050 aluminum alloy, with and without pre-heating, using the finite element method. This behavior has been studied by numerical simulation, using the software RADIOSS, which has a suitable formulation for inserting the effects of temperature and strain rate in the material. The results show a decline in the forces for electric hot incremental sheet forming preheated (EHISFP) compared to the electric hot incremental sheet forming (EHISF). Moreover, for these same cases, there was a gain in relation to the geometric precision on average more than 4%.     

轴铆自转速度和进给速度对轮毂轴承性能的影响

采用弹塑性有限元法对轮毂轴承轴铆成形过程进行研究。分析了轴铆接过程铆头的梅花运动规律,将铆头作为刚体处理,在仿真中实现轴向平移和平面梅花状复合运动,同时提高了计算精度和计算效率。对轮毂轴和内圈材料进行试验,确定了轮毂轴材料的弹塑性本构关系。研究不同自转速度与进给速度条件对轮毂轴承性能的影响,对梅花状加载轨迹的轴铆成形进行了应力应变分析。结果表明：随着铆头自转速度的提高,轮毂轴承预紧力先增大后趋于稳定,铆头的自转速度增至516 r/min后内圈径向变形达到峰值;当进给速度在某一范围内变化时,预紧力和内圈径向变形会出现峰谷值;提高自转速度或降低进给速度都能减小铆接力,铆接机振动减小,提高成形质量。     

卡车驱动桥壳体机械扩胀成形工艺分析及实验研究

提出一种适用于中型卡车驱动桥壳体制造的施加轴向辅助推力的机械扩胀成形工艺。推导了低于金属再结晶温度条件下方管坯极限扩胀成形系数的解析式,并对成形过程中各力参量的匹配对极限扩胀成形系数的影响规律进行了分析,给出了径向胀形时轴向辅助载荷的取值范围。根据所得出的理论,以某5t卡车驱动桥壳为研究对象,基于有限元软件DEFORM-3D对成形过程的关键工序进行了数值模拟,获得了金属流动状态、应力应变分布及壁厚的变化规律,并对桥壳在扩胀过程中出现缺陷的形式和部位进行了预测。在挤压设备上进行了相关的物理试验,结果表明轴向辅助载荷对于防止胀形过程中发生拉裂的必要性。实测了试验中合格样件的外形和壁厚分布,试验结果与有限元模拟结果吻合,从理论和实践上验证了机械扩胀成形工艺应用于制造中型卡车驱动桥壳的可行性。